KNOWLEDGE

How to better design the bag filter?

Steps for the selection (or design) of the bag filter

(1) Collect relevant data including purification gas characteristics, dust characteristics, purification indicators, the performance of various bag filters, and the selection or design of bag filters are generally carried out according to the following main steps.

(2) To select the form, filter material, and dust removal method of the bag filter, first determine the form of the dust collector.

①The bag filter is mainly used to control particles with a particle size of about 1 pm. When the dust-containing gas concentration exceeds 5g/m3, in order to reduce the filter load of the filter, it is best to adopt a secondary dust removal, that is, in front of the bag filter Add first-stage dust removals, such as cyclone dust collector or gravity sedimentation chamber;

②Not is suitable for purifying oil mist, water mist, dust with strong adhesion and high humidity. For example, when the amount of processed gas is not large, the purification efficiency is high, and the area of the plant is limited, and the investment, equipment ordering, and operation management are all conditions, the pulse jet bag filter, reverse airflow and mechanical rapping can be used. Dust-cleaning bag type dust collector, etc.

When the processing gas volume is large (such as 103m3/h or more), it can be considered to use a counter-flow dust-cleaning bag filter, etc. For small and medium-sized enterprises, the plant area is not restricted, investment, installation, and maintenance management are all

If there are certain difficulties, consider adopting a simple bag filter and mechanical vibration dust bag filter.

Secondly, choose the appropriate filter material. When selecting the filter material, the characteristics of the dust-containing gas (temperature, humidity, and corrosiveness) and technical and economic indicators should be considered. For example, when the gas temperature is 10~300℃, glass fiber filter bags can be used; when the dust is fibrous, nylon filters with a smoother surface should be used; for general industrial dust, polyester flannel filter bags can be used.

Then, determine the cleaning method. The ash removal method is the important basis for the selection. It is restricted by many factors such as dust viscosity, filtration speed, air resistance, pressure loss, purification efficiency, and so on. Therefore, the ash removal method should be determined according to the main constraints.

(3) Determine the filtration speed and filtration speed VR of the filter area-mounted dust collector, which refers to the average speed of the gas passing through the filter material, unit: m/min. The transition speed (also known as the size of the filter wind speed is an important indicator that determines the performance and economy of the dust collector, which can be calculated as follows:

V-filtration speed, m/min

Q—The air volume of bag filter m3/h

A-filter area, m2

Conversely, when the filtration rate is determined, the filtration area can be determined.

Too high a filtration rate will increase the resistance to compaction of the dust accumulated on the filter material sharply. Due to the increase of the pressure difference between the two sides of the filter material, the dust particles will penetrate into the filter material, even through filtration, resulting in an increase in the dust concentration at the outlet. This phenomenon is more obvious just after the filter material is cleaned. If the filtration speed is too high, a dust layer will quickly form on the filter material, which will cause too frequent dust removal and shorten the service life of the filter bag; if the filtration speed is low, the resistance will be low and the efficiency will be high; but if the filtration speed is too low, you need to If the filter area is too large, too large equipment is required, the equipment cost increases, and the equipment occupies a large area. Therefore, it is necessary to comprehensively consider factors such as dust characteristics, population dust concentration, flue gas temperature, filter properties, dust removal methods, and equipment resistance to determine the filtration speed.

(4) The dust collector is selected or designed with a finalized product, and the model and specification of the dust collector can be selected according to the processed gas quantity Q and the total filtering area A. If you need to design your own, you can follow the steps below.

①Determine the size of the filter bag, that is, determine the diameter D and height L. The diameter of the filter bag is generally D=100~600mm, usually D=200~300mm. Try to use the same specification to

It will be overhauled and replaced. The height of the filter building has almost no effect on the dust removal efficiency and pressure loss, generally 2-6m.

②Calculate the area of each filter bag.

a=DL

③Calculate the number of filter bags n

n=A/a

④ Arrangement and hanging of the filter bag. When the number of filter bags is required, the filter bags can be divided into several groups according to the cleaning method and operating conditions. The distance between two adjacent filter bags in each group is generally 0~70mm. The distance between groups and between the filter bag and the housing should consider the need to replace the filter bag and the inspection strip. The method of fixing and tightening the filter bag has a great influence on its service life. It is necessary to consider the convenience of bag replacement, maintenance, and adjustment, and to prevent the fixing part from wearing and breaking.

⑤ Shell design. Including dust collector box, inlet and exhaust duct form, ash hopper structure, manhole and operation platform, etc.

⑥The design of the dust removal mechanism and the determination of the dust removal system.

⑦The design of the dust conveying, recycling, and comprehensive utilization system, including the recovery of useful powder and preventing dust from flying again.

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